The present invention relates to a drive unit using a shape memory alloy, and particularly to a drive unit for moving a drive body to a specific operational position by using a shape memory alloy which exhibits superelasticity when energized.
A drive unit generally includes a shape memory alloy member made from a shape memory alloy containing titanium (Ti) and nickel (Ni) and a drive body connected to the shape memory alloy member, wherein the drive body is moved by energizing the shape memory alloy member.
FIGS. 7 and 8 show a related art drive unit xe2x80x9caxe2x80x9d using a shape memory alloy.
The drive unit xe2x80x9caxe2x80x9d is composed of a shape memory alloy spring xe2x80x9cbxe2x80x9d made from a shape memory alloy, a drive body xe2x80x9ccxe2x80x9d, and a bias spring xe2x80x9cdxe2x80x9d.
The shape memory alloy spring xe2x80x9cbxe2x80x9d is arranged such that one end is connected to the left side surface of the drive body xe2x80x9ccxe2x80x9d and the other end is fixed to a first fixing wall xe2x80x9cexe2x80x9d. The bias spring xe2x80x9cdxe2x80x9d is arranged such that one end is connected to the right side surface of the drive body xe2x80x9ccxe2x80x9d and the other end is fixed to a second fixing wall xe2x80x9cfxe2x80x9d.
The shape memory alloy spring xe2x80x9cbxe2x80x9d is electrically connected to a power source (not shown). When energized by the power source, the shape memory alloy spring xe2x80x9cbxe2x80x9d exhibits superelasticity, and is thereby contracted to move the drive body xe2x80x9ccxe2x80x9d in the direction A from a stopping position shown in FIG. 7 to an operational position shown in FIG. 8.
When the energization of the shape memory alloy spring xe2x80x9cbxe2x80x9d is released, the drive body xe2x80x9ccxe2x80x9d is returned in the direction B from the operational position shown in FIG. 8 to the stopping position shown in FIG. 7 by the biasing force of the bias spring xe2x80x9cdxe2x80x9d.
The above-described related art drive unit xe2x80x9caxe2x80x9d, however, has a problem. Since it is required to continue the energization of the shape memory alloy spring xe2x80x9cbxe2x80x9d for retaining the drive body xe2x80x9ccxe2x80x9d at the operational position, the power consumption becomes large. In particular, since the shape memory alloy containing Ti and Ni has a small inner resistance, the power consumption upon energization thereof becomes much larger. This brings a large obstacle to put the drive unit using the shape memory alloy into practical use.
The related art drive unit xe2x80x9caxe2x80x9d also causes the following inconvenience: namely, in the case of retaining the drive body xe2x80x9ccxe2x80x9d at the operational position by continuing the energization of the shape memory alloy spring xe2x80x9cbxe2x80x9d, the drive body xe2x80x9ccxe2x80x9d tends to be oscillated, resulting in wobbling of the drive body xe2x80x9ccxe2x80x9d at the operational position.
An object of the present invention is therefore to provide a drive unit using a shape memory alloy, which is capable of reducing the power consumption while overcoming the above mentioned problems.
To achieve the above object, according to the present invention, there is provided a drive unit using a shape memory alloy, including: a shape memory alloy member made from a shape memory alloy, the shape memory alloy member exhibiting superelasticity when being energized; a drive body connected to the shape memory alloy member, the drive body being moved from a stopping position to a specific operational position when the shape memory alloy member is energized; and a locking mechanism for retaining the drive body at the specific operational position.
With this configuration, since it is not required to continue the energization of the shape memory alloy member for retaining the drive body at the specific operational position, it is possible to significantly reduce the power consumption.
The locking mechanism may be provided with a locking portion, and the drive body may be integrally provided with a portion to be locked with the locking portion. With this configuration, it is possible to reduce the number of parts and to certainly retain the drive body at the specific operational position.
The locking mechanism may be additionally provided with a locking-releasing mechanism for releasing the retention of the drive body at the specific operational position. With this configuration, it is not required to provide a locking-releasing mechanism separately from the locking mechanism. Accordingly, it is possible to reduce the number of parts and simplify the mechanism, and hence to miniaturize the drive unit using a shape memory alloy and reduce the production cost of the drive unit.
The locking-releasing mechanism may be provided with an extensible/contractible member which is made from a shape memory alloy and exhibits superelasticity when being electrified, whereby the retention of the drive body at the specific operational position is released by energizing the extensible/contractible member. With this configuration, it is possible to easily control the locking-releasing mechanism and certainly release the locking state of the drive body, and hence to ensure the desirable operational state of the drive unit.
The drive unit may further include a bias spring, connected to the drive body, for retaining the drive unit at the stopping position. With this configuration, it is possible to certainly retain the drive body at the stopping position and hence to optimize the operation of the drive unit.